Judgement Errors in Medicine
Why the Problem Is Not About Knowledge
„Judgements do not arise from knowledge. They arise from what is accessible in the moment of judging.“
When we go to see a doctor, we trust that knowledge and experience will secure the right diagnosis. That is reasonable. It is just not the whole truth.
Because what makes medical decisions error-prone has less to do with missing knowledge than with how that knowledge is processed in the moment of judgement.
What the Referral Says
Prior diagnoses are not neutral information. They set a frame that determines how everything that follows is read. A clinician who sees a patient labelled "bronchitis" sees her through that label, not because anyone is careless, but because fast, intuitive thinking does exactly that. It categorises before conscious thinking has even begun.
In a documented case, a patient arrived in the emergency department with shortness of breath, cough and exertional dyspnoea. The referral said bronchitis, and the team treated accordingly. The pulmonary embolism that was actually present only came to light through an ultrasound performed for a different reason. The relevant signs were not entirely absent. They were read through an interpretation that had already been set.
In an analysis of 100 diagnostic errors in internal medicine, the most common contributing factor was not missing knowledge but faulty processing of information that was already available. A survey of 387 emergency physicians found that cognitive factors were involved in 96 per cent of all diagnostic errors, reflecting the normal condition of human judgement.
Why Experience Does Not Solve This
The intuitive assumption is that experience builds protection. Those who have seen more judge better. That is often true. But not always in the way we would like.
Experience makes pattern recognition faster. An experienced physician recognises connections in seconds that others would have to piece together with effort. That very strength becomes a weakness the moment the recognised pattern does not fit the case and analytical thinking fails to step in as a corrective, because the situation already feels familiar. The case no longer feels open. It feels already understood.
Subjective confidence in one's own judgement is systematically higher than actual accuracy, and this effect does not diminish with growing experience. Mamede and colleagues demonstrated this experimentally. Resident physicians who had previously worked a case with a particular diagnosis tended to favour the same diagnosis in a subsequent case with similar symptoms, even when it was objectively a poor fit. Recent experience had shifted the perception of probability without those involved being aware of it.
The feeling of certainty is not the same as the quality of the judgement.
How a Diagnosis Gains Weight
Diagnostic errors rarely arise from a single moment of flawed thinking. More often, it is a movement.
First, a piece of prior information sets the frame. It might be a triage note, a referral or a colleague's remark. New information is then fitted into that frame. What fits becomes visible. What does not fit registers as background noise. Once a plausible explanation has been found, the search ends earlier than it should. And once that explanation has been passed on several times, it no longer feels like a hypothesis. It feels like a finding.
A diagnosis does not become truer, but it becomes socially more stable.
That is dangerous, because people do not only respond to facts but to the confidence with which facts are presented. A diagnosis repeated across three handovers carries different weight from one that has just been floated as a possibility, even when both rest on the same evidence. A retrospective study found that 22 per cent of all ischaemic strokes in the emergency department were initially misdiagnosed, in a third of those cases still within the window for life-saving treatment. Assessments carried over without being actively questioned were a central factor.
The Problem Almost Nobody Knows
Cognitive biases describe systematic errors in one direction. But there is a second source of judgement errors that carries almost equal weight in the medical context and is almost never discussed.
Two psychiatrists independently diagnose 426 inpatients. They agree in 50 per cent of cases. In mammography, the false-positive rate among experienced radiologists assessing identical images ranged from 1 to 64 per cent. This is not a difference in competence but random variation in judgements that should be consistent. Kahneman calls it noise.
Time of day, fatigue, recent experiences and individual risk tolerance all influence judgements without those making them being aware of it. An internist who sees a clear need for action in the first patient of the morning with unclear symptoms, but no longer sees that need three hours and six consultations later in a patient with an almost identical presentation, is not judging worse than she was in the morning. She is judging differently, because cognitive fatigue is a real factor in judgement quality.
The treatment a person receives depends not only on their condition but also on who decides, when and where.
Why Hospitals Amplify the Problem
Cognitive biases arise in the individual. Their impact, however, is either limited or amplified by the system around those involved. In most hospitals, it is amplified.
Steep hierarchies are a central factor. When a senior physician puts forward a suspected diagnosis, it is rarely challenged in the morning handover, even when new findings point the other way. That is not a personal failing but a structural consequence. Who challenges whom? When is doubt legitimate? Which observation is significant enough to disturb an established direction? These questions are rarely explicitly settled, so they tend to be resolved socially.
There is also the fragmentation of the hospital itself. Nursing, medical staff, administration, social services, radiology, technical departments. Each professional group works in its own language, with its own routines and its own understanding of its role. A nurse may notice a change in a patient's behaviour that would be diagnostically relevant. A junior doctor thinks of an alternative explanation but does not voice it, because the direction already seems set. The knowledge is not gone, It just does not come together.
In teams with low psychological safety, this problem grows larger. Psychological safety means that people can raise concerns and dissenting assessments without fearing social consequences. Where that safety is absent, precisely those observations that could correct a judgement are held back. The result is not only flawed thinking but also relevant observations being raised less often, which prevents early course corrections and learning from mistakes.
What Would Need to Change
If judgement errors in medicine are substantially structural in origin, individual effort is not enough. What is needed are structures that take human cognition seriously and address it directly.
That begins with a question that is systematically absent from the diagnostic process. Not "What confirms this diagnosis?" but "What would make me abandon it?" The first question arises on its own. The second has to be actively built in, in handovers, in team meetings, in training, because it works against the natural pull of intuitive thinking.
Psychological safety is also needed as a leadership task. A senior physician who says in the morning handover that she is not sure about a case creates more space for critical thinking in the team than any training on cognitive biases. Uncertainty is then treated not as a weakness but as a realistic state of demanding judgement.
And there needs to be awareness of variation. Present the same case independently to two colleagues and compare their assessments. The variability is almost always greater than expected. That is not a reason for embarrassment but the starting point for a serious question. At which points does the judgement depend less on the facts than on the circumstances under which it is formed?
What I Find Important About This
I research and work on the question of how people judge under uncertainty and what distinguishes good judgements from poor ones. Medicine is for me one of the most striking fields for this, because the consequences of judgement errors are so immediately felt and because the belief that expertise alone protects against them is so persistent.
What genuinely concerns me is not that doctors make mistakes. All people who must judge under pressure do. What concerns me is that the structures in which they work make those mistakes invisible in many cases, rather than catchable. A wrong diagnosis is not only an individual error. It can be the result of a system in which early interpretations become stable too quickly, doubt is given too little space and dissenting observations do not come together in time.
I believe we can only think within the limits in which we are able to ask ourselves questions. A hospital that creates no space in which questions can be asked closes with it the space in which judgements can be examined.
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Reflection starts with dialogue.
If you’d like to share a thought or question, you can write to me at contact@lucalbrecht.com
Thinking from Scratch
by Luc Albrecht
Exploring how we think, decide and create clarity
